217 
A 
plants either with very little structure or with highly reticular 
venation. For many monocotyledonous plants some modifica- 
tion is necessary in the mechanical hypothesis, and curves more 
elongated in the direction of the current are obtained. 
Mr Srevey asked whether there was any corresponding law 
to be discovered for leaves which were not floating but aerial : 
he thought it might be possible to refer all leaves to such laws. 
With regard to the influence of pressure on growth in leaves, 
so long as it did not override vital force in the plant, he thought 
it fell in with what was to be observed in animal growth, which 
required intermission of pressure, for continuous pressure would 
stop growth. 
Mr Hern said that in the case of aerial leaves the problem 
was far more difficult, seeing that the water neutralized gravity 
and the edges of the leaves were more flexible. He had con- 
sidered that case a little, but preferred to discuss the simpler 
case first, with the hope of at some future time working out the 
more complex. He pointed out that there always was some 
little pressure on leaves from surface currents. 
Dr Pacur asked whether Mr Hiern had tested his theory by 
some simple experiments 4 
Professor CayLEy asked whether he had examined the effect 
on the leaves of the same plant in still and running water ? 
Mr Hiern said that the forms of leaves were apparently 
modified by circumstances, and that the experiments suggested 
would not be easy. 
On the effect of exhaustion and inflation of the tympa- 
num in deadening sounds, and on the test of loud- 
ness. By Mr Moon. 
The author discussed the problem “Why, when the tympanal 
cavity is either exhausted or inflated, low tones are more 
affected than high tones?” Before doing this he considered the 
ordinary explanation of what is the test of the loudness of a 
